Functional imaging through Single Photon Emission Computed Tomography (SPECT) has been shown to be effective for diagnosing and staging various types of cancer. However, a major limitation of SPECT imaging is its relatively poor spatial resolution and count statistics, which are influenced mainly by the collimator design. This is especially true for medium-energy and high-energy SPECT imaging, which is of particular importance for cancer imaging (particularly prostate cancer) and for infection imaging. At higher gamma ray energies, the lead collimator septa are required to be very thick because of the reduced attenuation coefficient. While much research has focused on detectors and image reconstruction, there have been virtually no advances in collimator technology in the past two decades. In this proposal, we will investigate the application of advanced materials technology to create SPECT collimators from ultra-high density materials. This will allow the use of thinner collimator septa, which will provide better resolution, sensitivity, and image quality. In Phase I, we will design and produce prototype segments of medium and high-energy collimators, and we will compare their imaging characteristics to those of standard lead collimators. This research will benefit all clinical applications of medium-energy and high-energy SPECT. PROPOSED COMMERCIAL APPLICATION: The proposed research will lead to higher-performance collimators for SPECT imaging and will have immediate commercial use as components for gamma cammera systems, both new and installed. This will allow for improved lesion detection for prostate cancer and other forms of cancer. The research will also be applicable to collimation and shielding components for PET, CT, and x-ray systems, as well as miscellaneous medical physics products.